You have an Exchange Server 2010 organization.  You need to recommend a client access solution that meets the following requirements： .Reduces the time required for users to reconnect to user mailboxes if a single Client Access server fails.Prevents users from being prompted for authentication if a single Client Access server fails What should you recommend？（）

• A、Client Access server array and hardware load-balancer
• B、database availability group （DAG） and hardware load-balancer
• C、failover clustering and database availability group （DAG）
• D、Windows Network Load Balancing and failover clustering